1. Field of the Invention
This invention relates to a four wheel steering system, more specifically to a rear wheel steering system of the four wheel steering system of a vehicle.
2. Description of the Related Art
It has been known a four wheel steering system of a vehicle in which a rear wheel is steered in accordance with a steering of a front wheel. In the four wheel steering system, it has been also known by for example, Japanese Patent Public Disclosure No. 57-44568, laid open to the public in 1982 that the steering of the rear wheel is made by an electric motor. According to the rear wheel steering system utilizing the motor disclosed in the Japanese Patent application, there is provided a return spring for returning the rear wheel from a position where stopped to a neutral position in an abnormal condition of the rear wheel steering system. The motor is connected with the rear wheel steering system through a clutch. When the abnormality occurs in the rear steering system, the clutch is disengaged so that the return spring returns the rear wheel to the neutral position.
It should however be noted that a resilient force of the return spring is not controllable. Therefore, When the rear wheel is returned to the neutral position, the steering condition of the vehicle may change undesirably abruptly so that vehicle operation is made unstable.